The present invention relates to a variable displacement compressor used for vehicle air conditioner, and more specifically, to a device and a method for controlling the displacement of a compressor.
In a general variable displacement compressor used for vehicle air conditioners, the inclination angle of a swash plate located in a crank chamber changes in accordance with the pressure in the crank chamber. The crank chamber is connected to a suction chamber, through a bleed passage, and to a discharge chamber, through a supply passage. The bleed passage is regulated by a displacement control valve. A controller, which includes a computer, controls the control valve to adjust the flow rate of refrigerant gas that flows to the suction chamber from the crank chamber through the bleed passage. As a result, the flow rate of gas leaving the crank chamber through the bleed passage changes relative to the flow rate of gas that is supplied to the crank chamber from the discharge chamber through the supply passage. The pressure in the crank chamber is adjusted, accordingly.
The control valve includes, for example, a valve body, a pressure sensing mechanism, which operates the valve body in accordance with the pressure in the suction chamber (suction pressure), and an electromagnetic actuator, which applies a force corresponding to the value of electric current supplied from the controller to the valve body. The force applied by the electromagnetic actuator reflects the target suction pressure. The controller adjusts the value of electric current supplied to the electromagnetic actuator to change the target suction pressure.
The controller increases the value of electric current supplied to the electromagnetic actuator to decrease the target suction pressure and decreases the value of electric current supplied to the electromagnetic actuator to increase the target suction pressure. When electric current is not supplied to the electromagnetic actuator, the target suction pressure is maximized.
When the suction pressure exceeds the target suction pressure, the pressure sensing mechanism operates the valve body to increase the opening size of the bleed passage. Therefore, the flow rate of refrigerant gas from the crank chamber to the suction chamber is increased and the pressure in the crank chamber is then lowered. This increases the inclination angle of the swash plate so that displacement of the compressor increases. When the displacement of the compressor increases, the cooling performance of a refrigeration circuit incorporating the compressor increases, and the suction pressure decreases toward the target suction pressure. When the suction pressure is lower than the target suction pressure, the pressure sensing mechanism operates the valve body to decrease the opening size of the bleed passage.
Therefore, the flow rate of refrigerant gas from the crank chamber to the suction chamber decreases and the pressure in the crank chamber increases. This decreases the inclination angle of the swash plate so that the displacement of the compressor decreases. When the displacement of the compressor decreases, the cooling performance of the refrigeration circuit is reduced and the suction pressure increases toward the target suction pressure.
Thus, the pressure sensing mechanism operates the valve body in accordance with the suction pressure to maintain the suction pressure at the target suction pressure.
The load on a vehicle engine increases when the vehicle is abruptly accelerated. Since the compressor is driven by the vehicle engine, if the engine load is great, the displacement of the compressor is temporarily minimized to reduce the engine load through a displacement limiting control procedure. Specifically, when a vehicle is abruptly accelerated, a controller changes the value of current supplied to the electromagnetic actuator to zero from a value that corresponds to the required cooling performance. As a result, the target suction pressure is maximized. Then, the pressure sensing mechanism of the displacement control valve closes the bleed passage with the valve body such that the actual suction pressure Psa approaches the maximum value. Thus, the pressure in the crank chamber increases and the inclination angle of the swash plate becomes minimum, which minimizes the displacement of the compressor. Therefore, the torque of the compressor is minimized and the engine load is reduced.
The displacement limiting control procedure is completed after a predetermined period from its start. After that, the controller starts a normal displacement control procedure in accordance with the cooling performance required for the refrigeration circuit. Specifically, the controller increases the value of current supplied to the electromagnetic actuator from zero to a value that corresponds to the required cooling performance. Accordingly, the target suction pressure is lowered from the maximum value to a value that corresponds to the required cooling performance.
If the target suction pressure is quickly maximized from a value that corresponds to the required cooling load when the displacement limiting control procedure is initiated, the actual suction pressure is temporarily much lower than the target suction pressure. The pressure sensing mechanism quickly shuts the bleed passage so that the actual suction pressure approaches the maximized target suction pressure. This suddenly increases the crank pressure and decreases the compressor displacement. As a result, the compressor torque is suddenly reduced, which suddenly reduces the engine load.
If the target suction pressure is quickly lowered from the maximum value to a value that corresponds to the required cooling performance when the displacement limiting control procedure is finished, the actual suction pressure is temporarily much higher than the target suction pressure. In this state, the pressure sensing mechanism quickly opens the bleed passage so that the actual suction pressure is lowered to the target suction pressure. This suddenly lowers the crank pressure and increases the compressor displacement. As a result, the compressor torque and the engine load are suddenly increased.
Sudden changes of the compressor displacement caused by sudden changes of the target suction pressure suddenly change the engine load. Accordingly, the vehicle performance and response are adversely affected.
Accordingly, it is an objective of the present invention to provide a displacement control device and a displacement control method for a variable displacement compressor that smoothly and rapidly shifts between a displacement limiting control procedure to a normal displacement control procedure.
To attain the above-mentioned object, the present invention provides a displacement control device for a variable displacement compressor used in a vehicle air conditioner. The compressor is driven by an engine and varies the displacement in accordance with the pressure in a crank chamber. The control device comprises a control valve for controlling the pressure in the crank chamber. The control valve includes a valve body and an electromagnetic actuator for applying a force to the valve body. The magnitude of the force corresponds to a value of a current supplied to the actuator. A power source supplies the current to the actuator. A switch device is located between the actuator and the power source. A controller determines a target value of the current supplied to the actuator in accordance with an external condition, wherein, when the target value is changed to a new value, the controller controls the switching of the switch device such that the current is intermittently supplied from the power source to the actuator before the current is set to the new target value.
The present invention also provides a method for controlling a displacement control device of a variable displacement compressor used in a vehicle air conditioner. The compressor is driven by an engine and changes the displacement in accordance with the pressure in a crank chamber. The method comprises controlling the pressure in the crank chamber with a control valve, wherein the control valve includes a valve body, an electromagnetic actuator for applying a force to the valve body, wherein the magnitude of the force corresponds to the value of current supplied to the actuator, and determining the target value of current supplied to the actuator in accordance with an external condition, and supplying the current to the actuator, and intermittently supplying the current to the actuator when the target value is changed before the current is adjusted to the new target value.
Other aspects and advantages of the invention will become apparent from the following description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the invention.